Latex is well known for its plasticizing, adhesive and film forming effects, either as a coating alone or as an ingredient in a coating composition. When latex is used as a component of cement and mortar compositions, it will generally provide the cured concrete with one or more improved properties such as tensile strength, compressive strength, flexural strength and water resistance, thereby resulting in a more durable, weatherproof and wear resistant surface that also may have resistance to penetration by water or corrosive liquids such as salt solutions. These latex modified cement and mortar compositions may be used for both new construction and restoration work. Paving compositions using latex modified Portland cement produce upgraded concrete pavement in so far as tensile, compressive, flexural and bond strengths are concerned. It has also been found that latex modified concrete pavement is generally more resistant than conventional concrete to penetration by water and salt solutions and generally is less susceptible to freeze-thaw effects and chemical attack even in thin strata such as 0.75 of an inch or 1 inch.
U.S. Pat. No. 2,662,064 discloses a composition containing Portland cement, fibrous and non-fibrous fillers and pigments, a rubbery styrene butadiene copolymer in latex form, and a water-soluble thickener selected from the class consisting of hydroxyethyl starch, dextrin, hydroxyethyl cellulose, and sodium carboxymethyl cellulose. This composition is designed for use as a decorative, sprayable wall surfacing material with good adhesion and abrasion resistant properties. The patent does not teach that the composition has the resistance to penetration by water or corrosive liquids desirable for example in surfaces exposed to freeze-thaw action or to the deteriorative effects of chemical substances used for ice or snow removal such as salt.
Polymer concrete type products which may be moldable are shown in U.S. Pat. No. 3,892,704 and are said to have increased strength and waterproof properties as well as a decreased tendency to develop efflorescence. In this case the polymer is formed by reaction of a water soluble ethenoid monomer, a water soluble crosslinking monomer, and a redox catalyst system in the presence of a water soluble alkali metal sulfate or carbonate. The cement product containing the polymer is found to cure more rapidly thereby producing concrete with improved properties.
Australian Pat. Specification No. 147,189 published Sept. 9, 1948, discloses a high alumina cement, an inert filler and a vinyl polymer emulsion to provide a well bonded shock resistant non-slip coating for metal, cement, wood or other subsurfaces.
U.S. Pat. No. 2,979,476 teaches bulk polymerization of styrene to obtain crystalline polystyrene containing wax. The wax must be added at between 15% and 60% conversion of the styrene monomer and the resultant product is a moldable composition employing fillers to obtain wear-resistant, sound-sensitive phonograph records.
U.S. Re. Pat. No. 28,722 discloses a cement mortar composition comprising Portland cement, mineral aggregate, a styrene-butadiene copolymer latex, water, a non-ionic surfactant, an anionic surfactant and a polyorganosiloxane fluid surfactant. The patent teaches that less water is required to obtain a workable cement mortar when the latex and surfactants are added. Improvements in such properties of the composition as flexibility, adhesion, elongation at break and volume change are also found.
U.S. Pat. No. 4,039,345 discloses an improved shrinkage compensating Portland cement concrete and mortar composition comprising an expansive Portland cement, mineral aggregate, a styrene-butadiene copolymer latex, water, a non-ionic surfactant, an anionic surfactant, a polyorganosiloxane foam depressant, and reinforcement to provide against expansion. The patent teaches improved properties for these compositions such as compressive and flexural strength, and freeze-thaw resistance. These compositions are especially suited for use in construction of crack-free structures.
U.S. Pat. No. 4,057,528 discloses a process for repairing concrete using cement mortar compositions capable of being pneumatically sprayed which provide enhanced bonding capabilities and resistance to slump. The cement mortar compositions comprise a substantially non-air entraining Portland cement, mineral aggregate, a styrene-butadiene copolymer latex, water and a polyorganosiloxane foam depressant.
None of the above prior art compositions teach the use of a latex that has the property of decreasing the penetrability of the coating or composition in which it is used to provide improved resistance to water and/or corrosive liquids.
The Federal Highway Administration has conducted research as described in Report No. FHWA-RD-77-16 entitled "Internally Sealed Concrete: Material Characterization And Heat-Treating Studies". This report shows the use of small spherical wax particles or beads mixed with the conventional components of Portland cement, the resultant concrete having a wax content of about 3% by weight. After the concrete is cured, heat is applied and the wax melts and flows into the capillaries and bleed channels of the concrete. The wax solidifies in these capillaries and interstices, creating an internally sealed concrete. However, it is believed that the time and expense required to melt the wax through the cured concrete pavement, the complex equipment required and the energy costs to melt the wax render such a procedure highly impracticable.